1. Field of the Invention
The present invention relates to a fuel spray apparatus for a gas turbine engine including a staged fuel injector composed of two combustion methods, i.e., a diffusion combustion and a lean-mixture combustion.
2. Background Art
In recent years, reduction of harmful substances, such as nitrogen oxide (NOx) and the like, discharged from a gas turbine has been strictly required for environmental protection. Meanwhile, for the gas turbine, especially for an airplane engine, good altitude relight ability has been required, and thus ability for low-NOx combustion as well as for stabilized combustion has attracted significant attention. Thus, the staged fuel injector composed of a single fuel injector valve incorporating the diffusion combustion system adapted for ensuring the stabilized combustion and the lean-mixture combustion system adapted for substantially reducing the NOx has been prevailed. More specifically, this staged fuel injector includes a pilot fuel supply system and a main fuel supply system, wherein fuel can be supplied from only the pilot fuel supply system or part, upon low power operation, thereby to perform more stabilized combustion under diffusion combustion condition, while the fuel can also be supplied from the main fuel supply system or part, upon high power operation, thereby to further reduce the NOx under lean-mixture combustion.
During a transition from the high power operation to the low power operation in the gas turbine including such a staged fuel injector, the fuel is supplied from only the pilot fuel supply system, while the supply of the fuel from the main fuel supply system is stopped. In order to prevent coking of the fuel remained in a fuel passage of the main fuel supply system (i.e., in a main fuel passage) due to high temperature air fed from a compressor during this transition, a fuel passage portion corresponding to the main fuel passage is covered with a shroud to provide an air heat insulating space or layer between this fuel passage portion and the shroud, or otherwise a separate fuel circuit for always flowing the fuel therethrough is provided to cool the fuel present in the main fuel passage (e.g., JP2007-183094A). However, such countermeasures cannot sufficiently address the problem of the coking as described above. For instance, the fuel remained in the main fuel passage may tend to be pushed out by the air entering the fuel passage and leak into surrounding parts or members, such as the shroud constituting the air heat insulating space. As a result, the fuel that leaks into the shroud will be carbonized due to contact with a high temperature wall of the shroud. Further, if such leakage of the fuel is continued and the amount of the carbonized fuel (or coking) is rather increased, the fuel passage will be connected with the shroud via the so-carbonized fuel, resulting in substantial degradation of the cooling effect due to the air heat insulating space. Thus, such coking of the fuel will be continued until the supply of the fuel from the main fuel supply system is actually stopped. This may cause a serious hindrance to a next injection operation of the fuel (or main fuel) from the main fuel supply system. To address this problem, more positive countermeasures against the unwanted leakage of the fuel into the surrounding members, such as by supplying suitable fluid or gas, e.g., purge air or the like, to the main fuel passage, at the same time that the stop operation of the supply of the main fuel is started, are now being studied.
However, such supply of the purge air as described above requires a high pressure pump, lines, valves and the like, respectively provided for exclusive use, thus inevitably increasing the number of such parts or members, rendering the entire system more complicated and substantially increasing the weight thereof.